1. Field of the Invention
The present invention relates generally to improved methods and compositions for sealing pipe strings in well bores, and more particularly, to such methods and compositions wherein the sealant is corrosion resistant, highly resilient and has high bond strength.
2. Description of the Prior Art
Hydraulic cement compositions are commonly utilized as sealants in subterranean well construction and repair procedures. For example, hydraulic cement compositions are used in primary sealing operations whereby strings of pipe such as casing and liners are sealed in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of the well bore and the exterior surfaces of pipe disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath supports and positions the pipe in the well bore and bonds the exterior surfaces of the pipe to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
When conventional cement compositions are utilized for sealing pipe strings in well bores, they set into brittle solid masses. Consequently, the solid cement often does not have sufficient resiliency to resist loss of pipe and/or formation bond, cracking or shattering as the result of pipe movements caused by expansion, contraction, impacts or shocks. The bond loss, cracking or shattering of the set cement allows leakage of formation fluids through at least portions of the well bore by way of the annulus therein which can be highly detrimental.
Hardenable epoxy resin compositions have heretofore been used for sealing pipe strings in well bores which penetrate subterranean zones containing corrosive fluids. For example, waste fluids such as salt water, acidic materials, caustic materials, organic materials, chemical by-product materials and the like are often disposed of by injecting them into disposal wells. Such disposal wells penetrate subterranean formations which accept large volumes of waste and are naturally separated from other subterranean formations. When a disposal well or other well where hydrocarbons are produced along with corrosive fluids is completed in the conventional manner whereby a string of steel pipe is cemented in the well bore utilizing a hydraulic cement slurry, both the cement and steel pipe are often subjected to severe corrosion. A result of such corrosion in disposal wells can be that the liquid waste materials leak into and contaminate formations containing useful fluids such as hydrocarbons or potable water. In other wells where hydrocarbons are produced with corrosive fluids, the corrosion can result in leakage of fluids between formations and/or to the surface.
In order to prevent the corrosion of metal pipe strings in disposal and other similar wells, it has heretofore been the practice to seal the pipe strings in well bores with a hardenable epoxy resin composition. Epoxy resin compositions are highly resistant to degradation by acids and other corrosive fluids and their use at least reduces the corrosion of metal pipe strings and the chances that corrosive fluids will find their way to the surface or into other subterranean locations. However, like set cement compositions, hardened epoxy resin compositions have often lacked sufficient resiliency as well as the necessary bond strength to resist failure as a result of pipe movements.
Thus, there are needs for improved methods and compositions for sealing pipe strings in well bores whereby the hardened compositions can withstand the effects of contact with corrosive fluids and also have the resiliency and high bond strength required to withstand pipe movements without failure.